Thoracic Aortic Aneurysm

I. What every physician needs to know.

The focus of this chapter is on thoracic aortic aneurysm. Abdominal aortic aneurysm is discussed in a separate chapter. An aneurysm is a dilation of an artery of at least 50% greater than the normal artery and can be either localized or diffuse.

Thoracic aortic aneurysm is divided into three types, dependent on the location:

Ascending Aorta - involvement from the aortic annulae to the innominate artery - is the most common.

Aortic Arch - includes involvement of the brachiocephalic vessels.

Descending Aorta - involvement distal to the left subclavian artery - is the second most common.

Some will also include thoracoabdominal aneurysm which is further categorized based on the Crawford classification as:

I. Proximal - descending thoracic to proximal abdominal aorta

II. Proximal descending to infrarenal aorta

III. Distal descending with abdominal aorta

IV. Primarily Abdominal Aorta

Thoracic aortic aneurysm comprise 25% of aortic aneurysms. Spontaneous rupture can occur leading to hemorrhagic shock. It is the eighteenth most common cause of death.

Risk factors and conditions that lead to weakening of the aorta include the following:

Family history (10% of patients with thoracic aneurysm have other family members with aortic aneurysm. Note that 21% of patients are without genetic connective tissue defect)

Computed tomography (CT) scan with contrast is the most commonly used diagnostic test to evaluate the thoracic aorta and the abdominal aorta. Spiral CT scan is critical to stent graft planning. It is able to evaluate the size of the thoracic aortic aneurysm, the extent of the disease, and the distal portions of the aorta. It is useful in unstable patients due to faster imaging times.

Magnetic resonance imaging (MRI) is an alternative in stable patients and is useful for long term surveillance due to lack of ionizing radiation. Gadolinium should be used with caution in patients with renal failure.

A. History Part I: Pattern Recognition:

Most patients are asymptomatic. Thoracic aneurysm is usually discovered after a chest X-ray or other radiographic study. The majority of patients have essential hypertension.

Screening for thoracic aneurysm involves obtaining a detailed family history to rule out genetic or familial disorders. Questions regarding family history of sudden cardiac death or history of aortic aneurysm is also included. An assessment for inflammatory or infectious conditions and screening for coronary artery disease is important.

Pain is the most common presenting symptom. The location of the pain may help localize the aneurysm. For example, anterior chest pain is usually associated with ascending aorta aneurysm. Neck pain may be associated with aortic arch aneurysm. Back pain between the scapula is usually a sign of descending aorta aneurysm.

B. History Part 2: Prevalence:

Thoracic aortic aneurysms occur in 3 to 4% of persons older than 65 years. The incidence of thoracic aneurysm is approximately 6 to 10 cases per 100,000 person years with the incidence of thoracic aneurysm rupture occurring in 3.5 per 100,000 persons. The average age of diagnosis is 69 years.

The prevalence of thoracic aortic aneurysm is up to 4.2% of the general population without hypertension. Most thoracic aortic aneurysms occur in the ascending aorta or the aortic arch. Aneurysm rupture accounts for 60% of deaths.

Degenerative aneurysm associated with advanced age most commonly seen. There is no difference between the incidence in males versus females. Arteriosclerosis is the most common cause of thoracic aneurysm involving the descending aorta and aortic arch. It is most common in older individuals with males affected more than females.

The etiology of thoracic aortic aneurysm is dependent on the location of the aneurysm. Ascending thoracic aorta aneurysm can be caused by cystic medial degeneration, genetics, familial, atherosclerosis, and infection such as syphilis.

Cystic medial degeneration occurs with aging and hypertension. Cystic medial necrosis is caused by the combination of protein degradation and mechanical factors. This leads to vessel dilatation and aneurysm formation.

Aortic aneurysm may be due to not only atherosclerosis but also Takayasu arteritis or as a continuation of an ascending and/or descending aortic aneurysm. Descending aortic aneurysm is most commonly seen in male persons aged over 55 years, associated with hypertension, hyperlipidemia, smoking, diabetes mellitus, familial or genetic diseases.

The role of atherosclerosis appears to be secondary to a multifactorial process which includes systemic and vascular structural proteins.

COPD and smoking are associated with thoracic aortic aneurysm and risk for aneurysm rupture. Hypertension, especially diastolic hypertension, is an independent risk factor for thoracic aortic aneurysm. Almost 25% of patients with a thoracic aortic aneurysm will also have an abdominal aortic aneurysm and slightly over 10% of persons diagnosed with an aortic aneurysm will have multiple aneurysms.

Genetics can play a role. Marfan syndrome is an autosomal dominant disorder and involves a mutation in FBN-1 gene which leads to abnormal fibrin and decreased tensile strength of the aorta. The majority of patients will have a dilated aortic root which may extend into the ascending aorta. Ehlers Danlos syndrome Type 4 involves a defect in Type III precollagen due to COL 3A 1 gene mutation. It is associated with aneurysms involving any portion of the aorta.

Familial factors with mutations in the transforming growth factor beta receptor 2 gene has been associated with thoracic aortic aneurysm and dissection. This is most common in first degree relatives of female patients with aneurysms.

Bicuspic aortic valve disease is the most common congenital heart disease in adults. It has been associated with tubular/ascending thoracic aortic aneurysm and sinus of Valsalva.

Loeys Dietz Syndrome involves a mutation to TBFBR1 or 2 gene and causes an aggressive vasculopathy and increased risk for aortic aneurysm.

Turner Syndrome has been associated with ascending aortic aneurysm as well as bicuspid valve and coarctation of the aorta.

Trauma such as motor vehicle accidents or fall from heights can lead to dissection at a point of fixation such as the aortic isthmus.

C. History Part 3: Competing diagnoses that can mimic Thoracic Aortic Aneurysm.

The differential diagnosis includes the following:

Acute myocardial infarction or Acute Coronary syndrome

Pneumothorax

Pulmonary embolism

Acute pericarditis

Pericardial effusion or tamponade

New aortic regurgitation

Penetrating Aortic ulcer

Aortic intramural hemorrhage

Esophageal rupture

Musculoskeletal or spinal pain syndrome

D. Physical Examination Findings.

Signs and symptoms are dependent on the location of the thoracic aneurysm. Most patients with thoracic aortic aneurysm are asymptomatic. The finding of a thoracic aortic aneurysm may be found incidentally during routine physical exam or chest x-ray.

Ascending aorta aneurysm present with chest pain or signs of myocardial ischemia or infarction due to compression of the coronary artery. There may be symptoms of obstruction of the SVC or symptoms of obstruction of right main bronchus. Physical exam findings may include heart failure due to aortic regurgitation, widened pulse pressure or diastolic murmur, or pulsating mass in the front of the chest. Sinus of Valsalva aneurysm may rupture leading to a continuous murmur and heart failure.

Aortic arch aneurysm may compress the trachea or ulcerate into the trachea causing radiating neck pain, wheezing, cough, hemoptysis, dyspnea, or pneumonitis. Hoarseness is due to involvement of the recurrent laryngeal nerve. Left lower lobe lung bronchus obstruction may cause atelectasis. Involvement of the phrenic nerve may cause hemidiaphragmatic paralysis.

Descending aorta aneurysm may present with back pain and lead to erosion of the vertebra. This may lead to neurologic symptoms of paraparesis or paraplegia. Pain may also be located in the mid-back or epigastric area. Dysphagia is due to compression on the esophagus and esophageal rupture can cause significant hematemesis. Emboli may involve distally to renal, visceral, or lower extremities.

Aneurysm rupture presents with severe pain, hypotension, and shock. The size of the aneurysm is the most important factor in determining the risk of rupture.

E. What diagnostic tests should be performed?

CT or MRI (more specifically CTA or MRA) are more specific compared to transesophageal echocardiogram (TEE) and can assess the size and extent of the aneurysm.

CT scan with contrast is the most commonly used diagnostic test to evaluate the thoracic aorta and the abdominal aorta. Spiral CT scan is critical to stent graft planning. It is able to evaluate the size of the thoracic aortic aneurysm, the extent of the disease, and the distal portions of the aorta. It is useful in unstable patients due to faster imaging times.

MRI and MRA are more time consuming but less nephrotoxic.

MRI is an alternative in stable patients and is useful for long term surveillance due to lack of ionizing radiation. Gadolinium should be used with caution in patients with renal failure. These tests are especially useful in patients with preexisting aortic disease and for aortic root aneurysms.

Echocardiogram has a role especially in aortic root aneurysm. Transthoracic echocardiogram (TTE) is performed first with TEE advocated if the initial study is incomplete or unable to provide sufficient data for the clinician. Echocardiogram is useful to assess for underlying valvular disease and evaluation of the aortic root. TEE is more sensitive but less specific than CT scan to assess the aorta especially the thoracic aorta and for the detection of dissection. TEE is able to exam the entire aorta and is preferred when dissection is suspected.

Aortography is rarely used and increasingly replaced by TEE and CT scans. Aortography may be useful to define the anatomy of the thoracic aortic aneurysm and the great vessels. However, it is unable to provide images of extraluminal aneurysmal size.

1. What laboratory studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

BUN and creatinine should be obtained to determine baseline renal function. CBC, prothrombin time, blood type and crossmatch should be obtained prior to surgery.

Liver function tests, amylase, lactate should be obtained in patient with acute dissection or distal embolization.

Chest X-ray may show widened mediastinum or aortic calcification and can lead a physician to suspect thoracic aneurysm.

2. What imaging studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

A discussion of the diagnostic tests are above in 'What diagnostic tests should be performed'. See Figure 1 and Figure 2 for radiographic images of CT and chest X-ray respectively.

Figure 1.

CXR showing descending thoracic aortic aneurysm.

Figure 2.

CT imaging showing thoracic aortic aneurysm.

F. Over-utilized or “wasted” diagnostic tests associated with this diagnosis.

For abdominal aorta dissection, research is underway looking for biomarkers, such as smooth muscle myosin heavy chain protein and other metalloproteinases.

III. Default Management.

The decision for surgical repair is dependent on symptoms, aneurysm size, and rate of growth of the aneurysm. Perioperative testing and risk stratification is recommended prior to elective repair.

In addition to the CT or MRI the following tests are usually recommended:

Baseline EKG and transthoracic echocardiogram should be performed to screen for valvular disease and assess cardiac function.

Dobutamine echocardiogram or dipyridamole stress test should be performed in persons with history or risk factors to assess for coronary artery disease or ischemia. Cardiac catheterization in persons over the age of 40 years or those persons with history of coronary artery disease may also be necessary.

Pulmonary function tests (PFTs) and ABG are recommended in persons with history of smoking or COPD.

Carotid US should be performed if a carotid bruit is heard on exam or in persons with history of TIA or stroke.

Brain CT or Brain MRI may be needed in persons with history of stroke or neurologic findings on exam.

If there is a history of claudication or if there are findings of decreased arterial pulses which suggest peripheral arterial disease, noninvasive lower extremity arterial study should be performed.

Intraoperative intravascular US and intraoperative epiaortic US is performed during the procedure.

A. Immediate management.

Preoperative management includes assessment for coronary artery disease and the need for concomitant CABG. The use of TEE to assess for aortic valve stenosis and aortic valve insufficiency as assessment for the need for aortic valve replacement. Finally, carotid ultrasound should be obtained to rule out carotid artery disease and CT scan brain obtained if there is a risk for stroke.

Emergent surgery is indicated for patients with symptoms of an acute aortic aneurysm rupture. There are two surgical options. The first surgical option is open surgical repair. Most commonly, aortic root aneurysm or ascending aortic aneurysm involve open surgery approach. The surgery involves replacement of the aneurysmal part with a dacron or woven graft. Aortic arch aneurysm involves use of branched graft as well as the need for coronary artery reimplantation and may also require aortic valve repair or replacement. Due to the need for access to the brachiocephalic, interruption of cerebral blood flow necessitates hypothermic circulatory arrest. Embolization of atherosclerotic material may lead to stroke.

Thoracic endovascular aortic repair (TEVAR) using stent grafting is an alternative for descending thoracic aortic aneurysm in high risk patient. Overall mortality is noted to be lower after TEVAR procedure as compared to open surgery. However, surgery is preferred in patients with Marfan disease or other connective tissue disease. Spinal cord injury and postoperative paraplegia may occur. These patients need close followup and serial CT scans to monitor for complications such as endoleak.

In 2010, Guideline Summary recommendations were outlined based on Joint Task force from the American College of Cardiology and the American Heart Association.

B. Physical Examination Tips to Guide Management.

Postoperatively, the patient should be monitored for signs and symptoms of myocardial infarction or coronary ischemia. Neurologic status should be monitored especially with surgery involving aortic arch aneurysm repair or descending aortic aneurysm repair. Paraplegia or paraparesis may occur following descending thoracic aorta aneurysm repair.

Complications of open surgery include hemorrhage, postoperative paraplegia from spinal cord ischemia, and stroke from cerebral ischemia.

Complications of endovascular repair include peripheral vascular complications including vascular trauma and thrombosis. Other complications include endoleaks, stent migration and fracture, and aortic reoperation.

The use of statins was associated with improvement in long term outcomes and reduction in thoracic aorta aneurysm repair. Statins should be titrated to the maximum dose tolerated. Statins appear to mediate inflammatory markers that may lead to aneurysm expansion.

Other steps to lower the risk include smoking cessation, healthy weight, exercise, blood pressure control, management of diabetes, and good cholesterol. Various aides are available to help with smoking cessation including nicotine replacement, buproprion, Chantix, and Varenicline.

Blood pressure should be controlled with the use of beta-blocker and vasodilators. Goal is systolic blood pressure 100-120 mmHg and heart rate 50-60. For acute dissection, first-line treatment with ultra-short-acting beta blockers, such as esmolol, is used particularly in patients with labile blood pressures because of its short duration of action. Labetalol, which blocks alpha-1, beta-1, and beta-2-adrenergic receptors, is also an option. A vasodilator such as nitroprusside is usually added in combination with a beta-blocker.

For long-term management, the following medications are used for treatment of hypertension. Beta-blockers should be titrated to effect with goal heart rate of less than 60 bpm. ACE inhibitor or ARBs should be titrated to blood pressure goal of less than 130/80. Calcium channel blockers may be used and titrated to goal. Beta-blockers and ACE inhibitors or ARBs are especially useful in the patients with Marfan syndrome.

Renal insufficiency and pulmonary dysfunction are major risk factors of surgical treatment for thoracic aortic aneurysm.

Postoperative monitoring for signs of myocardial ischemia or heart failure.

D. Long-term management.

Elective surgery is recommended for ascending aorta aneurysm size at 5.5 cm or descending aorta aneurysm size at 6.5 cm. The exception is patients with Marfan syndrome or familial aneurysm. These patients should undergo earlier repair with guidelines recommending ascending aortic aneurysm size at 5 cm or descending aorta aneurysm size at 6.0 cm. Rapid growth of a thoracic aneurysm greater than 0.5 to 1 cm/year is another indication for elective repair.

Evidence supports the recommendation for repair of large descending thoracic (thoracoabdominal) aneurysm greater than 5.5 cm or growth rate of greater than 0.5 cm/year. For patient with significant comorbidities, guidelines suggest repair at diameter of 6.0 cm.

Patients who have undergone endovascular graft repair for descending aortic aneurysm should have close followup and serial CT scans to monitor for complications such as endoleak.

There is a 5-year survival of 56% in patients with thoracic aortic aneurysms greater than 6 cm who do not undergo surgery. For patients who underwent emergent surgery, the 5-year survival rate was 37% compared to 85% 5-year survival rate in patients who underwent elective surgical repair.

Annual surveillance with imaging is recommended for diameters 3.5 cm to 4.4 cm, and semi-annual surveillance with imaging is recommended for diameters 4.5 cm to 5.5 cm.

E. Common Pitfalls and Side-Effects of Management.

Thoracic aorta aneurysm rupture and dissection are the principal cause of death. Mortality ranges from 50 to 80% once rupture occurs. The annual death rate for aneurysms less than 5.5 cm is approximately 5%.

Complications are variable. Due to loss of blood flow in the radicular artery, paraplegia at T10 can occur due to spinal ischemia.

Postoperative monitoring for signs of myocardial ischemia or heart failure.

For abdominal aortic dissection and blood pressure control, use of IV labetolol or esmolol in addition to IV nitroprusside is recommended. Sodium nitroprusside should not be used as monotherapy for abdominal aortic dissection.

Avoid beta-blockers in second or third degree AV block, fulminant heart failure, sinus bradycardia, and severe COPD with bronchospasm. IV Verapamil or IV Diltiazem may be substituted in these situations.

For long term management, the following medications are used for treatment of hypertension. Beta blockers should be titrated to effect with goal heart rate of less than 60 bpm. ACE inhibitor or ARBs should be titrated to blood pressure goal of less than 130/80. Calcium channel blockers may be used and titrated to goal.

Statins are titrated to the maximum dose tolerated.

Smoking cessation is encouraged and various aides are available including nicotine replacement, buproprion, Chantix, and Varenicline.

IV. Management with Co-Morbidities.

Persons diagnosed with Marfan syndrome should have an echocardiogram on presentation and followup echocardiogram 6 months later to assess for enlargement. First degree relatives of a person with thoracic aorta aneurysm or aortic dissection should have aortic imaging. Any person who has symptoms that suggest thoracic aorta dissection should have immediate radiologic imaging.

Contraindications for surgery are dependent on the risks/benefits ratio and comorbidities such as age, end stage renal disease, respiratory insufficiency and cirrhosis.

Postoperative complications include bleeding, stroke, ARDS, and MI.

A. Renal Insufficiency.

There is little data concerning the management of patients with chronic renal insufficiency who are undergoing aneurysm repair.

Preoperative hydration is recommended to assure euvolemia.

Renal dysfunction may occur due to prolonged cross clamping or hypothermic circulatory arrest. Predictors of post-operative renal dysfunction are preoperative renal function, cross clamp time, and repair extending to the renal arteries. Intraoperative use of furosemide or mannitol is not beneficial in reducing postoperative renal insufficiency.

ACE inhibitors and ARBs should be held if creatinine is greater than 2.3. ACE inhibitors and ARBs should be held on the day of surgery and restarted when the patient is euvolemic.

Metformin should be held preoperatively, especially with concomitant use of contrast dye. Contrast induced nephropathy (CIN) may occur. The incidence of CIN can be reduced with intravenous hydration.

B. Liver Insufficiency.

Risk for bleeding and coagulopathy are important factors to address. Low hemoglobin and low hematocrit is associated with increased mortality following aneurysm repair. A platelet count less than 130,000 platelets/uL was associated with an increased risk of bleeding. A history of varices, gi bleeding, and hepatic encephalopathy should be obtained.

Platelet count, PTT, PT, INR, and hemoglobin/hematocrit should be obtained prior to any surgery. Platelet count needs to be above 50 and INR needs to be less than 1.5.

C. Systolic and Diastolic Heart Failure.

Echocardiography is recommended for patients which history of dyspnea or heart failure.

D. Coronary Artery Disease or Peripheral Vascular Disease.

Preoperative assessment for coronary artery disease (CAD) and aortic valve disease should be undertaken prior to surgery to determine if concomitant CABG or aortic valve replacement is needed.

Recent history of bare metal stent or drug-eluting stent is a factor regarding the timing of the surgical intervention.

It is important to assess for recent MI, decompensated heart failure, arrhythmia, or severe valvular heart disease. In these cases, coronary angiography may be necessary.

Noninvasive cardiac testing is recommended only if it will change management. Patients capable of METS > 4 generally do not need further cardiac testing. Patients who cannot achieve this level of activity or who have other risk factors may benefit from noninvasive cardiac testing if it will change management.

An EKG is recommended for all patients undergoing aneurysm repair. Echocardiogram is recommended for patients which history of dyspnea or heart failure.

Postoperatively, patient should be monitored for signs or symptoms of myocardial infarction or coronary ischemia.

If there is a history of claudication or if there are findings of decreased arterial pulses which suggest peripheral arterial disease, noninvasive lower extremity arterial study should be performed.

E. Diabetes or other Endocrine issues.

Blood glucose should be closely monitored. Conventional glucose control is recommended.

Metformin should be held due to risk of nephrotoxicity.

F. Malignancy.

An evaluation of the risk factors and comorbidities should be addressed.

The recent use of chemotherapy or radiation therapy should be known.

The type of cancer and prognosis are important areas to discuss.

G. Immunosuppression (HIV, chronic steroids, etc).

Persons on chronic steroids should be considered for stress dose steroids.

H. Primary Lung Disease (COPD, Asthma, ILD).

There is an association between aneurysm and COPD. It is imperative that the COPD management be optimized prior to surgery. ABG and PFTs should be obtained. Smoking cessation at least 2 weeks prior to surgery is recommended.

Bronchodilators should be administered at least 2 weeks prior to surgery in patients with symptomatic COPD or abnormal PFTs.

ARDS may occur postoperatively.

I. Gastrointestinal or Nutrition Issues.

Monitoring of gastrointestinal bleeding in persons with history of esophageal or gastric ulcer.

NG tube decompression should be used intraoperatively. The NG tube should be discontinued postoperatively in the majority of patients.

Nutrition should be optimized.

J. Hematologic or Coagulation Issues.

Low hemoglobin and low hematocrit is associated with increased mortality following aneurysm repair. A platelet count less than 130,000 platelets/uL was associated with an increased risk of bleeding. Therefore, it is important to monitor hemoglobin/hematocrit and monitor for coagulation abnormalities. In patients with a history of MI, studies recommend transfusion for hematocrit less than 28%.

K. Dementia or Psychiatric Illness/Treatment.

Due to loss of blood flow in the radicular artery, paraplegia at T10 can occur due to spinal ischemia.

V. Transitions of Care.

A. Sign-out considerations While Hospitalized.

B. Anticipated Length of Stay.

Average length of stay is 7 days for open aortic aneurysm repair but may be as long as 2 to 3 weeks. The length of stay is usually less in patients undergoing endovascular repair and usually averages 2.2 to 5 days.

On average, patients usually need 4 to 6 weeks to recover. For patients who have undergone open aortic aneurysm repair, the average recovery may be as long as 3 months. The average recovery time for patients who have undergone endovascular repair is less and is usually 1 to 2 weeks. However, if comorbidities, such as CAD, COPD, or CKI, or if extensive surgery was required, recovery may take 2 to 3 months.

C. When is the Patient Ready for Discharge?

Patients are ready for discharge when able to ambulate.

Blood pressure should be well-controlled.

D. Arranging for Clinic Follow-up.

CT scan or MRI should be obtained every 3 to 6 months postoperative for the first year, then every 6 months thereafter.

Echocardiogram should be obtained every 3 to 6 months for the first year postoperative ascending aorta aneurysm repair, then every 6 months thereafter.

1. When should clinic follow up be arranged and with whom.

Followup with Cardiothoracic surgeon should be arranged every 3 to 6 months postoperative for the first year and should coincide with obtaining the recommended imaging studies.

Blood pressure and hyperlipidemia should be monitored by the primary care physician.

Smoking cessation is emphasized.

2. What tests should be conducted prior to discharge to enable best clinic first visit?

Followup with Cardiothoracic surgeon should be arranged every 3 to 6 months postoperative for the first year and should coincide with obtaining the recommended imaging studies.

3. What tests should be ordered as an outpatient prior to, or on the day of, the clinic visit?

CT or MRI every 6 months.

Echocardiogram every 3 to 6 months for patients who underwent repair of ascending aorta artery repair.

E. Placement Considerations.

If comorbidities, such as CAD, COPD, or CKI, or if extensive surgery was required, recovery may take 2 to 3 months.

F. Prognosis and Patient Counseling.

At discharge, patients are restricted in terms of their physical activity. They should be instructed to avoid heavy lifting. Blood pressure should be monitored. Dietary restrictions, to control diabetes and hyperlipidemia, should be followed.

There is a 5-year survival of 56% in patients with thoracic aortic aneurysms greater than 6 cm who do not undergo surgery. For patients who underwent emergent surgery, the 5-year survival rate was 37% compared to 85% 5-year survival rate in patients who underwent elective surgical repair.

Patients who have had repair of ascending aorta or aortic root aneurysm repair may require reoperation due to aortic valve stenosis or insufficiency, acute dissection, prosthetic valve endocarditis, or aneurysm formation.

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